1. Field of the Invention
The present invention relates to an escapement governor equipped with an escape wheel, a balance with hairspring, and a pallet fork transmitting the power of the escape wheel to the balance with hair spring (roller), and to a mechanical watch; further, the present invention relates to a method of manufacturing a pallet fork (incomplete) constituting the frame of a pallet fork (complete), and a method of manufacturing a roller used with a pallet fork (incomplete).
2. Description of the Related Art
There exists a club tooth lever type escapement governor for a mechanical watch. In a known construction of such an escapement governor, in assembling a pallet fork (incomplete) and a safety pin, there is provided a round hole extending through the pallet fork (incomplete), and a shaft portion of the safety pin is forced into this round hole. The pallet fork (incomplete) and the safety pin are used together with a roller. More specifically, the safety pin enters a passing hollow provided in the roller, and allows rotation of the pallet fork (incomplete). Further, the safety pin abuts a portion of the roller other than the passing hollow, thereby preventing erroneous rotation of the pallet fork (incomplete). This safety pin is provided at an end portion of the pallet fork (incomplete), and is formed so as to protrude perpendicularly with respect to the pallet fork (incomplete). Near the safety pin, the pallet fork (incomplete) is provided with a pair of entry horn and exit horn. The pair of entry horn and exit horn collide with an impulse pin provided on the roller with a predetermined timing, whereby the pallet fork (incomplete) is caused to make normal or reverse rotation.
In connection with the roller, there is known a roller table called a single roller. The single roller consists of a single circular plate which is provided with a passing hollow. The single roller is provided with an impulse pin as mentioned above (See “The Theory of Horology”; Swiss Federation of Technical Colleges, (2005), pages 102 to 103 (FIGS. 6 through 13, and FIGS. 6 through 15), [ISBN: 2-940025-12-6].
Further, there has also been disclosed an integrally molded type pallet fork (complete) including a pair of entry horn and exit horn and a safety pin (See JP-A-2004-309480).
In the pallet fork (complete) as disclosed in JP-A-2004-309480, the safety pin is in the same layer as the pallet fork (incomplete), so that the thickness of the pallet fork (complete) as a whole including the pallet fork (incomplete) is advantageously small; however, since it employs a double roller, in which the impulse pin and the passing hollow are arranged in different layers, there is a limit to a reduction in the thickness of the escapement governor including the pallet fork (complete) and the double roller.
On the other hand, in the technique as disclosed in “The Theory of Horology” mentioned above, there is used a single roller, and a reduction in the thickness of the peripheral structure thereof is achieved; however, since the safety pin is formed so as to protrude perpendicularly with respect to the pallet fork (incomplete), a reduction in the thickness of the pallet fork (complete) cannot be achieved, so that, also in this technique, there is a limit to a reduction in the thickness of the escapement governor.
In this connection, as described above, in JP-A-2004-309480, the safety pin is formed so as to extend longitudinally toward the roller of the pallet fork (incomplete), which helps to achieve a reduction in the thickness of the pallet fork (complete) as a whole; thus, by applying this pallet fork (complete) to the single roller as disclosed in “The Theory of Horology,” it might be possible to contribute to a reduction in the thickness of the escapement governor.
However, the arrangement of the safety pin and the pair of entry horn and exit horn provided on the pallet fork (incomplete) as disclosed in JP-A-2004-309480 and of the passing hollow and the impulse pin of the single roller of “The Theory of Horology” mentioned above respectively corresponding thereto, is rather inappropriate, so that the pallet fork (incomplete) does not rotate appropriately, thus failing to exert its function as the pallet fork (complete).
More specifically, the safety pin as disclosed in JP-A-2004-309480 extends longitudinally toward the roller of the pallet fork (incomplete), and is formed to be longer than the pair of entry horn and exit horn. On the other hand, the single roller as disclosed in “The Theory of Horology” is constructed such that the impulse pin and the passing hollow are situated in that order away from the rotation center of the roller. As a result, the passing hollow is provided nearer to the safety pin than the impulse pin. Thus, despite the fact that the safety pin extends longitudinally toward the roller of the pallet fork (incomplete), the passing hollow used in correspondence thereto is provided at a position near the safety pin, so that the safety pin abuts the passing hollow, and the safety pin is caught by the passing hollow, making it impossible for the pallet fork (incomplete) to rotate properly.
Further, in the pallet fork (complete) of JP-A-2004-309480, the safety pin is longer than the pair of entry horn and exit horn, and the center of gravity thereof is far from the rotation center of the pallet fork (complete), so that the moment of inertia of the pallet fork (complete) increases, resulting in an increase in energy consumption in the escapement governor.